This application is related to a phosphorus acid catalyst for the preparation of 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphospha spiro [5,5] undecane.
As shown in U.S. Pat. No. 3,192,242, 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphospha spiro [5,5] undecane (SPDC) is a useful intermediate for the preparation of effective flame retardants, especially 2,2-bis(chloromethyl) 1,3-propylene bis[bis(2-chloroethyl) phosphate]. Later, U.S. Pat. No. 3,968,188 claims that certain catalysts effectively convert mixtures of pentaerythritol and phosphorus trichloride to SPDC. ##STR1## More particularly, U.S. Pat. No. 3,968,188 suggests that SPDC can be obtained by reacting pentaerythritol with a trivalent phosphorus trihalide in the presence of halides of metals of Groups I and II of the Periodic Table, tertiary amines and heterocyclic nitrogen-containing compounds.
The entire disclosures of the above-mentioned U.S. Pat. Nos. 3,192,242 and 3,968,188 are expressly incorporated herein by reference.